Certain salts of N-phosphonomethylglycine are effective as post-emergence herbicides. A commercial herbicide contains the isopropylamine salt of N-phosphonomethylglycine.
N-Phosphonomethylglycine can be made by a number of methods. One such method, as described in U.S. Pat. No. 3,160,632 is to react N-phosphinomethylglycine(glycinemethylenephosphonic acid) with mercuric chloride in water at reflux temperature, and subsequently separating the reaction products. Other methods are phosphonomethylation of glycine and the reaction of ethyl glycinate with formaldehyde and diethylphosphite. The latter method is described in U.S. Pat. No. 3,799,758. In addition, there is a series of patents relating to the preparation of N-phosphonomethylglycine, including U.S. Pat. Nos. 3,868,407, 4,197,254 and 4,199,354.
Close prior art is U.S. Pat. No. 3,923,877, which teaches the reaction of 1,3,5-tricyanomethylhexahydro-1,3,5-triazine with excess disubstituted phosphite to form (RO).sub.2 P(O)CH.sub.2 NHCH.sub.2 CN (R is hydrocarbyl or substituted hydrocarbyl) which is hydrolyzed to yield N-phosphonomethylglycine.
Because of the commercial importance of N-phosphonomethylglycine salts as herbicides, improved methods of preparing N-phosphonomethylglycine are valuable.